The overall objective of the proposed research is to further our knowledge of the cellular and membrane aspects of calcium-dependent neurotransmitter release. Liposomes will be used to deliver to nerve terminals substances, known or suspected to be physiologically active, which are difficult or impossible to study otherwise because of absence of such a delivery system. Improving the targeting of reagents to neural tissue could someday prove useful for the development of treatments for some classes of neurological diseases. The proposal will exploit the combined expertise of our laboratories, electrophysiology (presynaptic function at frog motor nerve endings) and membranology (development and applications of liposomes). It is designed to answer the following questions: 1) What are the optimal conditions for delivering the encapsulated contents of liposomes to motor nerve endings? 2) What is the mechanism by which liposomes deliver their contents to motor nerve terminals? As a corollary, what is the significance, with respect to the function of the participating nerve membrane, of its interaction with the liposomal membrane? 3) Is Ca entry required for evoked ACh release or for facilitation of ACh release? 4) Is the cellular selectivity for Ca, Sr and Ba intrinsic to the process of evoked ACh release or does it reflect the displacement of Ca from storage sites? This question is particularly important with respect to Ba, which is used in patch clamp studies. 5) Are second messenger systems (e.g., inositol tris phosphate, calmodulin, synapsin I) involved in modulation of neurotransmitter release?